//===----------------------------------------------------------------------===//
//                         DuckDB
//
// duckdb/transaction/duck_transaction_manager.hpp
//
//
//===----------------------------------------------------------------------===//

#pragma once

#include "duckdb/transaction/transaction_manager.hpp"
#include "duckdb/storage/storage_lock.hpp"
#include "duckdb/common/enums/checkpoint_type.hpp"
#include "duckdb/common/queue.hpp"

namespace duckdb {
class DuckTransaction;
struct UndoBufferProperties;

//! CleanupInfo collects transactions awaiting cleanup.
//! This ensures we can clean up after releasing the transaction lock.
struct DuckCleanupInfo {
	//! All transactions in a cleanup info share the same lowest_start_time.
	transaction_t lowest_start_time;
	vector<unique_ptr<DuckTransaction>> transactions;

	void Cleanup() noexcept;
	bool ScheduleCleanup() noexcept;
};

//! The Transaction Manager is responsible for creating and managing
//! transactions
class DuckTransactionManager : public TransactionManager {
public:
	explicit DuckTransactionManager(AttachedDatabase &db);
	~DuckTransactionManager() override;

public:
	static DuckTransactionManager &Get(AttachedDatabase &db);

	//! Start a new transaction
	Transaction &StartTransaction(ClientContext &context) override;
	//! Commit the given transaction
	ErrorData CommitTransaction(ClientContext &context, Transaction &transaction) override;
	//! Rollback the given transaction
	void RollbackTransaction(Transaction &transaction) override;

	void Checkpoint(ClientContext &context, bool force = false) override;

	transaction_t LowestActiveId() const {
		return lowest_active_id;
	}
	transaction_t LowestActiveStart() const {
		return lowest_active_start;
	}
	transaction_t GetLastCommit() const {
		return last_commit;
	}

	bool IsDuckTransactionManager() override {
		return true;
	}

	//! Obtains a shared lock to the checkpoint lock
	unique_ptr<StorageLockKey> SharedCheckpointLock();
	unique_ptr<StorageLockKey> TryUpgradeCheckpointLock(StorageLockKey &lock);

	//! Returns the current version of the catalog (incremented whenever anything changes, not stored between restarts)
	DUCKDB_API idx_t GetCatalogVersion(Transaction &transaction);

	void PushCatalogEntry(Transaction &transaction_p, CatalogEntry &entry, data_ptr_t extra_data = nullptr,
	                      idx_t extra_data_size = 0);

protected:
	struct CheckpointDecision {
		explicit CheckpointDecision(string reason_p);
		explicit CheckpointDecision(CheckpointType type);
		~CheckpointDecision();

		bool can_checkpoint;
		string reason;
		CheckpointType type;
	};

private:
	//! Generates a new commit timestamp
	transaction_t GetCommitTimestamp();
	//! Remove the given transaction from the list of active transactions
	unique_ptr<DuckCleanupInfo> RemoveTransaction(DuckTransaction &transaction) noexcept;
	//! Remove the given transaction from the list of active transactions
	unique_ptr<DuckCleanupInfo> RemoveTransaction(DuckTransaction &transaction, bool store_transaction) noexcept;

	//! Whether or not we can checkpoint
	CheckpointDecision CanCheckpoint(DuckTransaction &transaction, unique_ptr<StorageLockKey> &checkpoint_lock,
	                                 const UndoBufferProperties &properties);

private:
	//! The current start timestamp used by transactions
	transaction_t current_start_timestamp;
	//! The current transaction ID used by transactions
	transaction_t current_transaction_id;
	//! The lowest active transaction id
	atomic<transaction_t> lowest_active_id;
	//! The lowest active transaction timestamp
	atomic<transaction_t> lowest_active_start;
	//! The last commit timestamp
	atomic<transaction_t> last_commit;
	//! Set of currently running transactions
	vector<unique_ptr<DuckTransaction>> active_transactions;
	//! Set of recently committed transactions
	vector<unique_ptr<DuckTransaction>> recently_committed_transactions;
	//! Transactions awaiting GC
	vector<unique_ptr<DuckTransaction>> old_transactions;
	//! The lock used for transaction operations
	mutex transaction_lock;
	//! The checkpoint lock
	StorageLock checkpoint_lock;
	//! Lock necessary to start transactions only - used by FORCE CHECKPOINT to prevent new transactions from starting
	mutex start_transaction_lock;
	//! Mutex used to control writes to the WAL - separate from the transaction lock
	mutex wal_lock;

	atomic<idx_t> last_uncommitted_catalog_version = {TRANSACTION_ID_START};
	idx_t last_committed_version = 0;

	//! Only one cleanup can be active at any time.
	mutex cleanup_lock;
	//! Changes to the cleanup queue must be synchronized.
	mutex cleanup_queue_lock;
	//! Cleanups have to happen in-order.
	//! E.g., if one transaction drops a table, and another creates a table,
	//! inverting the cleanup order can result in catalog errors.
	queue<unique_ptr<DuckCleanupInfo>> cleanup_queue;

protected:
	virtual void OnCommitCheckpointDecision(const CheckpointDecision &decision, DuckTransaction &transaction) {
	}
};

} // namespace duckdb
